Date: Tue, 10 Dec 1996 17:33:10 GMT
Server: NCSA/1.4.2
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<title>Color Perception and Correcting for Chromatic Induction</title>
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<h1>Color Perception and Correcting for Chromatic Induction</h1>
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<h4>Research in progress, joint with Corin Anderson, Evan McLain, David
Salesin, and Dani Lischinski</h4>


In human vision, the perceived color of an object does not depend solely
upon the physical light that leaves the surface of that object.  Many other
factors play a role in the perceived color, including the color and brightness
of surrounding objects.  This is most clearly noted in the image below:<p>

<img src="images/blocks.gif" alt="[Image of obvious color shifts]"><p>

Believe it or not, the two center gray boxes are the same color,
although they clearly do not appear to be so.  This is due to
<em>chromatic induction</em> (actually, it is brightness induction,
but that subtly doesn't matter a whole lot here).  Automatically
correcting (<i>i.e.</i> removing) this effect is the topic of our
research.<p>

As motivation for this research, consider the case where the image below
were your company logo:<p>

<img src="images/logo_half.gif" alt="[Image of gray company logo]"><p>

If you were to compose your logo with the image below on the left, you would
generate an image like that shown below and on the right:<p>

<img src="images/colors_half.gif"
alt="[Green field on top, yellow field on bottom]">
<img src="images/ugly_half.gif"
alt="[Composite image:  gray logo looks red on top, blue on bottom]"><p>

This is an undesireable effect -- your company logo is supposed to be all
gray, not red on top, green on bottom, and blue on the side!  So you must
somehow correct this problem.<p>

One method of correction is simple avoidance: never put your company logo
on any strongly colored backgrounds.  The problem with this solution is
that you are now restricted with what you can do with your company's logo.
The second solution is to hand-correct your company's logo.  That is, with
the knowledge that the top of your logo will become reddish, you could add
green to your logo, and balance the chromatic induction.  While this
solution works for simple cases such as the one above, consider, the case
below, where the background color changes widely and smoothly.  It would
be difficult to guess what the resulting induced effects would be:<p>

<img src="images/spots_half.gif" alt="[Logo on mottled  background with
smooth color transitions]"><p>

The third alternative is to have a computer automatically correct for
chromatic induction, letting you have complete freedom of design with your
company's logo.  This is what our research is doing.  Our goal is to
design a program whose input is the graphic artist's image, where colors
are specified by what color <em>should be perceived</em> at each point.
The program would compute how the design elements will interact with each
other by chromatic and brightness induction, and adjust the image
accordingly.  The output would be an image whose <em>physical</em> colors
may be different than the input's, but whose <em>perceived</em> colors
would be what the graphic artist specified.<p>

<address>corin@cs.washington.edu</address>
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